a significant difference between
     these modes and <symbol>INV_READ</symbol> alone: with <symbol>INV_READ</symbol>
     you cannot write on the descriptor, and the data read from it will
     reflect the contents of the large object at the time of the transaction
     snapshot that was active when <function>lo_open</function> was executed,
     regardless of later writes by this or other transactions.  Reading
     from a descriptor opened with <symbol>INV_WRITE</symbol> returns
     data that reflects all writes of other committed transactions as well
     as writes of the current transaction.  This is similar to the behavior
     of <literal>REPEATABLE READ</literal> versus <literal>READ COMMITTED</literal> transaction
     modes for ordinary SQL <command>SELECT</command> commands.
    </para>

    <para>
     <function>lo_open</function> will fail if <literal>SELECT</literal>
     privilege is not available for the large object, or
     if <symbol>INV_WRITE</symbol> is specified and <literal>UPDATE</literal>
     privilege is not available.
     (Prior to <productname>PostgreSQL</productname> 11, these privilege
     checks were instead performed at the first actual read or write call
     using the descriptor.)
     These privilege checks can be disabled with the
     <xref linkend="guc-lo-compat-privileges"/> run-time parameter.
    </para>

    <para>
     An example:
<programlisting>
inv_fd = lo_open(conn, inv_oid, INV_READ|INV_WRITE);
</programlisting>
    </para>
</sect2>

<sect2 id="lo-write">
<title>Writing Data to a Large Object</title>

<para>
     <indexterm><primary>lo_write</primary></indexterm>
     The function
<synopsis>
int lo_write(PGconn *conn, int fd, const char *buf, size_t len);
</synopsis>
     writes <parameter>len</parameter> bytes from <parameter>buf</parameter>
     (which must be of size <parameter>len</parameter>) to large object
     descriptor <parameter>fd</parameter>.  The <parameter>fd</parameter> argument must
     have been returned by a previous <function>lo_open</function>.  The
     number of bytes actually written is returned (in the current
     implementation, this will always equal <parameter>len</parameter> unless
     there is an error).  In the event of an error, the return value is -1.
</para>

<para>
     Although the <parameter>len</parameter> parameter is declared as
     <type>size_t</type>, this function will reject length values larger than
     <literal>INT_MAX</literal>.  In practice, it's best to transfer data in chunks
     of at most a few megabytes anyway.
</para>
</sect2>

<sect2 id="lo-read">
<title>Reading Data from a Large Object</title>

<para>
     <indexterm><primary>lo_read</primary></indexterm>
     The function
<synopsis>
int lo_read(PGconn *conn, int fd, char *buf, size_t len);
</synopsis>
     reads up to <parameter>len</parameter> bytes from large object descriptor
     <parameter>fd</parameter> into <parameter>buf</parameter> (which must be
     of size <parameter>len</parameter>).  The <parameter>fd</parameter>
     argument must have been returned by a previous
     <function>lo_open</function>.  The number of bytes actually read is
     returned; this will be less than <parameter>len</parameter> if the end of
     the large object is reached first.  In the event of an error, the return
     value is -1.
</para>

<para>
     Although the <parameter>len</parameter> parameter is declared as
     <type>size_t</type>, this function will reject length values larger than
     <literal>INT_MAX</literal>.  In practice, it's best to transfer data in chunks
     of at most a few megabytes anyway.
</para>
</sect2>

<sect2 id="lo-seek">
<title>Seeking in a Large Object</title>

<para>
     <indexterm><primary>lo_lseek</primary></indexterm>
     To change the current read or write location associated with a
     large object descriptor, call
<synopsis>
int lo_lseek(PGconn *conn, int fd, int offset, int whence);
</synopsis>
     This function moves the
     current